Electric furnace.



P. A. BOECK.

ELECTRIC FURNACE. ArPucATmN man Nov.2. 191x.

1,158,971. Patented Nov. 2, 1915.

AltarneJ/J UNITED STATES PATENT OFFICE.

PERCY A. BOECK, 0F WORCESTER, MASSACHUSETTS, ASSIGNOR T0 NORTON COMPANY, 0F WORCESTER, MASSACHUSETTS, A CORPORATION 0F MASSACHUSETTS.

ELECTRIC .'FURNACE.

To Zt Iwhom it may concern Be it known that I, PnRcY A. Benen, a citizen of the United States, residing at lVoicestei', in the county of Torcester and State of Massachusetts, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

This invention relates to electric furnaces, the primary object of the invention being the provision of a furnace core or support for the resistance element, of a form and material adapted to afford a better distribution and more economical utilization of the heat than heretofore.

My improved electric furnace core consists essentially of a cup-shaped vessel or receptacle formed of a very refractory material of high thermal conductivity, said vessel having a helical groove on the exterior face of its sides or walls and a spiral groove in the lower face of its bottom, these groove-s merging to form a continuous groove for the reception of the resistance wire or element. f

An electric furnace core constructed in accordance with this invention is illustrated in the accompanying drawing wherein:

Figure l is a side elevation of the core; Fig. 2 is a bottom view thereof; and Fig. 3 is a central vertical section of the core, showing also the resistance element, the covering therefor', and a crucible in position in the core.

In said drawings, l represents the furnace core or support for the resistance element, the core having, in the particular form illustrated, a cylindrical wall 2, having formed in its outer face a helical groove 3, in which is laid a resistance wire l, which may be of nickel-chromium alloy, platinum, or other suitable material. This wire is preferably formed, before being wound upon the core, into a continuous coil or helix, which is then wound in the grooves in the manner indicated in Fig. 3. This construction presents the particular advantages that the length of the resistor can be indefinitely increased, while at the same time the liability of breakage is minimized. The bottom 5 is formed integral with the sides and provided with a spiral groove 6 on its lower surface, this groove 6 merging with the helical groove 3 aS shown at 7, Figs. 1 and 2,

Specification of Letters Patent.

Application filed November 2, 1911.

Patented Nov. 2, 1915.

serial No. 658,091.

The core, with the resistance element wound thereon, is covered with a thick layer of refractory cement, as shown at S in Fig. 3; and the whole is covered by a casing' 9, which may be of iron. Between the refractory cement 8 and the casing 9 is a filling l0 preferably consisting of pounded magnesia, this filling constituting an electrical and thermal insulator. The ends of the resistance element 4 protrude in order that they may be connected in the electric circuit, a convenient arrangement being as shown in F ig. 3, wherein the lower end of the wire extends directly downward from the center of the bottom of the core and through an aperture 1l in the bottom of the casing 9. A crucible in position to be heated is shown at 12. In use the open end of the core is usually covered by any refractory and heat-retaining material.

The refractory cement or composition S which covers the resistance element Ll is preferably composed of previously molten alumina grains, and a relatively small proportion, say five to fifteen per cent. or somewhat more, of a suitable bond, as for example plastic clay, or lime or magnesia. A composition of this character presents very important technical advantages for use in this connection: in particular it is chemically inactive with respect to the resistor and preserves the wire from corrosion; and by reason of its high thermal conductivity it conducts the heat rapidly from the resistor, thereby preventing overheating and consequent injury. At the same time it aids in the even distribution of heat throughout the core. Furthermore, by reason of the high specific heat of the cement it is adapted t0 serve as a heat accumulator or equalizer, preventing unduly large fluctuations of the interior temperature when the cover is removed or when articles are introduced into or removed from the furnace. It will be understood that a cement of this character may also be used in connection with any suitable core or support other than that herein described and claimed.

A furnace core constructed as herein described possesses several advantages: The distribution of the resistance element is such as to provide a substantially even temperature within the core, and the coils or turns of the resistance element are rmly held; at the same time the walls in contact with the necessary refractory character, possesses high thernlal conductivity. rSuitable materials .for the purpose are preyiously molten alumina grains bonded by frittingg' together or by the use of a small proportion of a refractory ceramic bond; and silicid of carbon, bonded by recrystzillization or otherwise. Such ma Leriais have a far higher thermal conductivity than porcelain or lire-clay,A

and are found to be durable and highly ellicient.

I claim tl. iin electric furnace comprising' a receptacle having' an open end, a helical groove formed in the outer surface of the body of said receptacle, and a spiral groove in its closed end, said grooves merejinp,` at the edge of the receptacle to form a continuous groove, and a resistor Within said groove and having' its ends projecting' respectively from opposite ends thereof.

2. An electric furnace comprising a recepnissen tacle haring an open end, a helical groove formed in the outer surface of the body of said receptacle, and a spiral eroove in its closed end. said Q,'rooves merging at the edge of the receptacle to form a continuous groove, a resistor within said groove and lia ving' its ends projecting' resljectively from opposite ends thereof, a refractory envelop of high thermal conductivity covering said resistor, and a, heat-retainingpacking surrounding said envelop.

'i electric :furnace comprising a recepiiaving' an open end, a helical groove in the outer surface of the body of l ixceptacle, and a spiral groove in its l, end, said grooves merging' at the edge Vhe receptacle to form a continuous kgroove. a resistor within said groove and haring' its ends projecting' respectively from opposite ends thereof, a refractory envelop covering' said resistor and comprising' previously molten alumina, and a heat-retaining pacli'ne' surrounding said envelo'i).

ln alli); my signature `whereof,

BOEVK.

in presence of two witnesses.

PERCY fs.. llvitnesses 2 Lons C. liAnLn C.

llieeixs, liilonsn.

Copies of this patent may be obtained for ve cents each, by addressing the Commissioner of Patents, Washington, D. C. 

